It is often desirable to produce sulfonates by reacting an aromatic compound with sulfuric acid. In many cases, this provides two or more aromatic sulfonates, at least one of which is preferentially oil soluble and at least one of which is preferentially water soluble. In U.S. Pat. No. 2,764,548, which is owned by the assignee of the present application, there is described a process for the production of dinonylnaphthalene monosulfonates. The salts of the monosulfonates are relatively highly soluble in oils, and form compositions having exceptional rust-inhibiting properties. It is also disclosed in the patent that the sulfonation of dinonylnaphthalene with sulfuric acid also produces the corresponding disulfonic acid, and this is described to be accumulated in an aqueous, spent acid layer which is later separated and discarded. Because under common commerical conditions the predominant product is the monosulfonate, the disulfonate has been treated as a byproduct, and wasted. In connection with this, disposal of this wasted product has been an economic and environmental problem because of a tendency to deteriorate the quality of water into which the waste is dispersed. It has now been found that dinonylnaphthalene disulfonic acid is useful in its own right, for example, as a textile processing surfactant and as a wetting agent. In particular, the salts of the disulfonic acid are useful as hydrotropes, in that they help to make clear solutions of petroleum or hydrocarbon solvents in water. The disulfonic acid is also useful in metal and equipment degreasing in combination with water only or as an additive for steam. A somewhat analogous problem is encountered in the sulfonation of didodecylnaphthalene, and also in the corresponding benzene analogs.
It is an objective of the present invention to provide a novel means of countercurrently washing and extracting a reaction mixture of an aromatic compound, sulfuric acid and a solvent to isolate a sulfonate, which, in the case of dinonylnaphthalene disulfonic acid, was formerly discarded a waste e product, in pure forms and thus provide new marketable items. It is an important feature of this invention, that the waste acid layer in U.S. Pat. No. 2,764,548 is treated in such a way that the valuable disulfonic acid product can be recovered, while at the same time upgrading the quality of the spent acid layer to a degree where it can be safely disposed of by addition to environmental waters. Of course, other sulfonation processes will also benefit from the present invention.